The goal of this project is to decipher cell type-specific crosstalk of signaling pathways in hematopoiesis and hematological diseases. This application is compelled by our new and surprising data indicating that two well-known signal regulators, Pten and Shp2, can work cooperatively or antagonistically in different blood cell lineages. Thus, the outcome of signal interplay in different cell types cannot be simply deduced from previously known functions for each molecule. Shp2 is a non-receptor tyrosine phosphatase possessing two SH2 domains that promotes Erk signaling, and dominantly activating mutations in PTPN11/Shp2 have leukemogenic effect. Ablating Shp2 suppressed hematopoietic stem cell (HSC) and progenitor cell proliferation and differentiation in mice, defining a positive role of Shp2 in hematopoiesis. In contrast, Pten (phosphatase and tensin homolog) is a tumor suppressor that negatively regulates the PI3K/Akt pathway and is frequently mutated in human leukemia. Targeted deletion of Pten resulted in dramatic expansion of short-term HSCs (ST-HSCs), excessive myeloid cell proliferation and development of leukemia. To test whether Pten and Shp2 have directly opposing functions in leukemogenesis, we generated conditional Pten and Shp2 double knockout (DKO) mice. Preliminary data suggest that additional deletion of Shp2 indeed suppressed excessive myeloid cell proliferation and leukemia induced by Pten-deficiency as expected, but surprisingly the Pten and Shp2 DKO mice developed lethal anemia. These results argue that although Shp2 and Pten have antagonistic roles in myeloid cells, these two regulators act in concert to promote red blood cell (RBC) development and maturation. This application seeks to elucidate the opposing as well as cooperating functions of Shp2 and Pten in blood cells. We will elucidate the molecular mechanisms underlying the cell type-specific crosstalk of Shp2- and Pten-modulated signals. The success of this project will not only advance our understanding of the interactive molecular pathways driving hematopoiesis in mammals, but also suggest better therapeutic strategies for leukemia and anemia.